Fata
Morgana Mirage Imaged by David Cartier (photography) on 20th February above the Tetlin
Hills of Eastern Alaska.

When light from hills or other distant objects
is refracted between layers of
very cold dense air overlaid by warmer air it forms a 'superior mirage'.
Superior because the image is above the real object.

Images can be strongly stretched vertically forming apparent cliffs or
fantastical towers - this is a 'Fata Morgana' named
after King Aurthur's enchantress half sister.

As here, the mirage changes not only with time but with your own height
relative to the air layers.

Mirages at sunset produce incredible sunshapes and their vertical magnification
is essential to form green flashes.